The invention relates to television camera automatic setup systems, and particularly to a pattern recognition circuit integral with an error measurement system, for reliably distinguishing between three possible pattern configurations within a diascope pattern, one example being the spatial location of nine white-to-black coarse locator configurations.
Automatic setup systems such as that of the U.S. Pat. No. 4,326,219 of previous mention, include means for performing spatial, shading, beam level, focus, etc., error measurements on the scan raster of pickup tubes in a television camera. To make such measurements it is necessary to identify the location of the scanning beam on the test pattern, that is, to assure that a specific portion of the test pattern is being scanned for each given error measurement. For example, when making coarse spatial error measurements, the above prior art system used a series (i.e., five) coarse registration locator rectangles placed at the center, at the top and bottom, and at either side, of the conventional optical test pattern, i.e., the diascope pattern, within the active video picture area. A locator detector circuit thereof includes detection and timing circuits and, inter alia, makes a coarse comparison of the locator positions in the diascope pattern relative to an electronic test pattern, to correct for gross centering, size and rotation scan errors. In addition, the system provides an output indicative of the detection of the checker transitions during the valid scanning by the beam of a selected block of checkers. The locator detector circuit supplies any errors detected during the setup mode to a memory of the camera control unit microprocessor via a data bus. Coarse scan corrections are then performed during the camera operating mode by a digital to analog converter and/or spatial error correction (SEC) circuitry such as depicted in the U.S. Pat. No. 4,354,243, upon retrieving the errors from the memory.
Such a pattern recognition and error detection system operates in the frequency domain utilizing the relatively larger size of the coarse locators relative to the checkers, i.e., four to one, as a basis for distinguishing the different pattern configuration. The use of the size ratio as the criterion to detect the locators via filtering and level detecting techniques in the frequency domain, does not prove reliable under adverse scanning conditions. For example, in the prior system, the coarse locator provides the locator strobe signal which is used to latch the coarse error into the system memory. It follows that in adverse setup conditions, when the beam scans at a greater angle due to picture skew, etc. in the region of the last locator, the circuit sometimes generates an erroneous locator strobe pulse from a white-to-grey transition rather than from the white-to-black transition. Detecting such a white-to-grey transition is possible if the beam scans from the white portion of a locator to the grey band area of the test pattern used for gamma correction. Thus, the pattern recognition and error measurement technique of the prior art provides marginal reliability, unless undesirable elaborate filtering techniques are utilized.